The present invention relates to polycarbonates and to a method of preparing same.
Polycarbonates are generally produced through one of two types of processes: an interfacial process or a melt transesterification process. In the melt transesterification process, dihydroxy compounds such as biphenol A are reacted with a carbonic acid diesters. For many purposes, the carbonic acid diester may be a diaryl carbonate such as diphenyl carbonate.
It is also known to use the melt transesterification process with activated diaryl carbonates. For example, U.S. Pat. No. 4,323,668 describes a polycarbonate transesterification process comprising reacting (ortho-alkoxycarbonylaryl)carbonates and a dihydric phenol under transesterification reaction conditions. In the specific examples, U.S. Pat. No. 4,323,668 makes uses of bis-methylsalicylcarbonate (BMSC) as the diaryl carbonate. Use of activated diaryl carbonates is also described in U.S. Pat. No. 6,420,512, U.S. Pat. No. 6,506,871, U.S. Pat. No. 6,548,623, U.S. Pat. No. 6,790,929, U.S. Pat. No. 6,518,391, US 2003/0139529, and US 2003/0149223. When these activated carbonates are used, internal residues and end-caps derived from the activated diaryl carbonate are incorporated into the final polymer. See, US patent Publication No. 20030050427 and 20030149223.